JP2000168737A - Hermetical sealing of paper container, and forming device using the same method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perfectly apply a hermetical sealing by eliminating an unevenness in heating even when a paper container has a sealing section wherein the quantity of aluminum foil layers is different by using a seal jaw for which ferrite is partially embedded in a high frequency coil section. SOLUTION: For a seal jaw 20 which seals with high frequency a cylindrical sleeve wherein a paper board is made the base material, and which comprises a laminated sheet wherein the innermost layer is a polyester based resin, the intermediate layer is an aluminum foil, and the outermost layer is a polyolefin based resin, and at the bonded section on which a skive process is applied, pressurizing block plates 21 and 22 at the high frequency coil sections 23 and 24 of which, ferrites 25 and 26 are partially embedded, are used. When a hermetical sealing region is inserted between the pressurizing block plates 21 and 22, the cylindrical sleeve is set in such a manner that the sections where the ferrites 25 and 26 are embedded may come into contact with a hut-sealing upper sheet 15a of a superposing region. By this constitution, the section constituted with 5 layers at the top sealed section is heated as well to a proper degree, and the overall sealed section is uniformly heated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a paperboard as a base material,
A sealing and sealing method in a molding and filling apparatus for molding, filling and sealing a cylindrical paper container comprising a laminated sheet having a polyester resin layer as an innermost layer, an aluminum foil layer as an intermediate layer, and a polyolefin resin layer as an outermost layer; The present invention relates to a mold filling and sealing device that executes the method.More specifically, it enables uniform sealing by eliminating uneven heating due to the difference in the number of aluminum foil layers due to folding of laminated sheets during molding into paper containers The present invention relates to a high-frequency sealing method and a molded filling sealing apparatus for executing the method.

[0002]

2. Description of the Related Art Paper containers comprising a laminated sheet of paper as a base material and an inner layer and an outer layer of a polyolefin resin having excellent heat sealing properties are widely used as containers for filling juice, milk, sake and the like. In particular, for contents such as sake, which have high permeability and a long circulation period, if the paper end surface is exposed on the inner surface of the container, the contents will penetrate into the paper base layer from there, causing a decrease in container strength. One of the laminated sheet body joining portions is removed from the paper layer by half the thickness of the laminated sheet from the front end by a predetermined length, and the remaining half of the thickness is folded from the inside to the removed portion from the inside to the outside,
Generally, the paper edge is protected. This processing is called skive processing.

[0003] The body of the laminated sheet subjected to skiving is joined by performing a frame treatment using a gas burner or the like from the folded inner layer surface portion to the outer layer surface portion, and further corresponding to the inner layer surface at the other end. In general, a similar flame treatment was performed to oxidize the surface of each polyolefin resin to introduce a polar group, and then press-bond both.

[0004] In addition, the laminated sheet formed into a sleeve by joining the body is preheated with hot air or the like at one end of the sleeve, and then immediately folded and pressed into a predetermined shape to form a container bottom. . Then, after filling the formed laminated sheet with the contents, the other end of the sleeve is similarly pressed and sealed while being heated to a predetermined shape to form a paper container filled with the contents. It was a target.

[0005] However, polyolefin resins used for the inner and outer layers of general paper containers are excellent in processability,
It has the drawback of having an oxidizing odor of the resin due to the influence of heat during film formation, and of easily adsorbing content components and flavors.It is particularly unsuitable for whiskey and mineral water, which are contents that value the taste. there were.

On the other hand, a polyester resin having a low odor and a low odor, which has a low resin odor, a low flavor adsorption, and a heat sealing property, has been developed. By using this polyester resin for the inner surface of the container, paper containers have come to be used for contents such as whiskey and mineral water that emphasize taste.

[0007] However, the above-mentioned skiving is necessary for highly permeable contents such as whiskey. In joining the body, both the polyester resin surface portion of the inner layer and the polyolefin resin surface portion of the outer layer that are folded back to the outer layer side are simultaneously thermally fused with the inner polyester resin surface of the other end. . In addition, the bonding between the bottom and the top involves heat fusion between the polyester resin surfaces of the inner layer, or between the polyester resin surface of the inner layer and the polyolefin resin surface of the outer layer.

As a sealing method in this case, a method of pre-heating with hot air and then pressure bonding with a pressure plate or a conventional high-frequency sealing method has been studied. The former method uses a polyester resin as a sealant layer. Melting with hot air and solidification or crystallization of the polyester resin by the time of compression bonding in the next step makes perfect sealing difficult.
In the latter method, the aluminum foil layer partially overlaps, so that only that part is not sealed,
It is difficult to seal uniformly because other parts are burnt.

Further, the polyester resin and the polyolefin resin are not fused together simply by heat. However, the surface of the polyolefin resin is subjected to a flame treatment using a gas burner or the like to oxidize the polyolefin resin surface and introduce polar groups. And heat-sealing with a polyester resin (disclosed in JP-A-3-227620). However, when the surface of the polyester resin is oxidized by the flame treatment, the heat fusion property between the polyester resins is hindered. Therefore, a skilled technique and time are required for adjusting the position of the gas burner for performing the flame treatment.

[0010]

SUMMARY OF THE INVENTION The present invention comprises a laminated sheet comprising a paperboard substrate, a polyester resin layer as an innermost layer, an aluminum foil layer as an intermediate layer, and a polyolefin resin layer as an outermost layer. One end of the joining part is made to solve the above-mentioned problems related to the method of hermetically sealing the bottom and top of a tubular paper container that has been subjected to skive processing. It is an object of the present invention to provide a high-frequency sealing method and a high-frequency sealing method in which non-uniform heating due to the difference in the number of aluminum foil layers is eliminated by partially embedding the shape according to the folded shape of the container.

[0011]

Means for Solving the Problems A first invention of the present invention is:
Using a paperboard as a base material, the innermost layer is a polyester resin layer, the intermediate layer is an aluminum foil layer, the outermost layer comprises a laminated sheet provided with a polyolefin resin layer, the inner sheet at one end of the laminated sheet, and the other A method for hermetically sealing a tubular paper container in which an end outer layer is joined by heat sealing, wherein one of the joined portions of the laminated sheet tubular portion is a predetermined length from the front end, and is half the thickness of the laminated sheet. Is removed from the paper layer, the remaining portion is folded from the inside to the outside of the removed portion, and the paper container hermetic seal method in which the paper end surface is protected, wherein the hermetic seal method is a high frequency seal method using a high frequency seal device. Then, as a seal jaw of the high-frequency sealing device, a seal jaw in which ferrite is partially embedded in a high-frequency coil portion is used, and innermost layers of the paper container or innermost layers are used. A hermetic sealing method of a paper container, which comprises sealing by the outermost high-frequency sealing method.

[0012] The second invention is the first invention, wherein
The high frequency sealing device is characterized in that ferrite is partially embedded in the sealing jaws on both the jaw side of the high frequency sealing device on which the high frequency coil is mounted and the receiving jaw on which the high frequency coil is not mounted to perform high frequency sealing. Is the way.

[0013] In a third aspect based on the first aspect,
A method for hermetically sealing a paper container, wherein ferrite is embedded in a sealing jaw according to the folded shape of the paper container.

According to a fourth aspect of the present invention, there is provided a first, second, or third aspect.
An apparatus for forming a paper container using the hermetically sealing method according to any one of the above.

As described above, according to the present invention, the innermost layers of the paper containers or the innermost layer and the outermost layer of the paper containers are sealed by high frequency using the sealing jaws in which the ferrite is partially embedded in the high-frequency coil portion. The bottom or top is completely sealed. In addition, since the ferrite is partially embedded in the seal jaws of both the jaw side of the high-frequency sealing device where the high-frequency coil is mounted and the receiving jaw side where the high-frequency coil is not mounted, the bottom or top of the paper container is completely Is applied. Furthermore, since the ferrite is embedded in the seal jaws according to the folded shape of the paper container, the bottom or top of the paper container is more completely sealed.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for hermetically sealing a paper container according to the present invention will be described below in detail based on one embodiment. FIG. 1 is a perspective explanatory view of a seal jaw according to an embodiment of the present invention. FIG. 2A shows the movement of the seal jaw of the hermetic seal in FIG.
FIG. 2B is an explanatory diagram viewed from a cross section taken along the line A-A ′, and FIG.
It is explanatory drawing of the seal jaw seen from BB 'cross section.

First, a base sheet used in the hermetic sealing method of the present invention is a laminated sheet comprising a paperboard as a base material, a polyester resin layer as an innermost layer, an aluminum foil layer as an intermediate layer, and a polyolefin resin layer as an outermost layer. Sheets can be used preferably. It should be noted that a barrier film in which a thin film of a metal compound such as silicon oxide or aluminum oxide is formed on the surface of a polyethylene terephthalate film by a method such as a vacuum deposition method on the surface of a polyethylene terephthalate film, which causes dielectric heating by high frequency instead of the aluminum foil layer. good.

The laminated sheet is punched into a desired shape using a generally used flatbed-type punching machine while inserting a predetermined bending line to form a blank for a paper container. When processing the blank into a tubular sleeve so that the paper at the end is not exposed, one of the joining portions that become cylindrical is removed from the paper layer by half the thickness of the blank by a predetermined length from the tip, and the remaining A so-called skiving process is performed in which the bent portion is folded from the inside to the outside removed portion.

In the tubular paper container, the skived blank is processed into a tubular sleeve by a method such as a frame processing method, for example, as shown in FIG.
The side wall plates 1, 2, 3 and the side wall plate 4
A tubular side wall portion A made of a connecting plate 5 which is adhered to a side end portion and which has the end portion on the liquid contact side which is connected to the side wall plates 1 and 4 to form a rectangular cylindrical body and which is skived; A is formed of a cylindrical sleeve S for a paper container having a top seal portion T having a flat surface formed on the upper portion A and a bottom seal portion B below the side wall portion A (see FIG. 4A). It is obtained by folding the seal portion B into a flat shape to form a hermetic seal.
The form of the paper container may be a so-called gable-top type having a roof shape other than the flat shape shown in FIG. 5D.

As shown in FIG. 5 (a), the top seal portion T is connected to one of the side wall plates 1, 3 and the side wall plate 4 of the side wall portion A, and is provided at the inner end of the side wall plate 1. Upper plates 11 and 13 connected to the upper portions of the attached connecting plates 5 respectively.
The connecting upper plate 15, the upper plates 11, 13 and the connecting upper plate 1
5 are attached to the palms 11a, 13
a, a palm top plate 15a and a folding isosceles triangular plate 1 provided on the other opposing side wall plates 2 and 4 of the side wall portion A;
2, 14; connecting triangular plates 12a, 12a connected to the upper side of the isosceles triangular plate 12;
4, a connecting triangular plate 14a continuously provided on an isosceles upper side,
14a, a plurality of connected palm-attached plates 12b, 12b connected to the upper side of the connecting triangular plate, and a plurality of linked palm-attached plates 14b, 14b.

When the top sealing portion T is hermetically sealed, first, as shown in FIG.
14 are folded inward (inward direction P ₁ ), the upper plate 11 and the upper plate 13 are brought into contact with each other so as to be horizontal, and as shown in FIG. Attached boards 11a and 13a to be superposed
And the upper end plate 15a attached to the upper end plate 11a at the side end connected to the side wall plate 4, and the inwardly connected palm attached plates 12b, 12b and the inwardly folded palm attached plates 14b, 14b.
Is thermally fused by using a sealing jaw 20 composed of a pair of pressure block plates 21 and 22 (see FIG. 5C) described later, which can be pressed and separated from each other from both sides of the superimposed surface. by wearing, sealed sealing the top seal portion T, 5 rafter clad plate 11a which is erected seal top seal portion T as shown in (d), 13a horizontally as an arrow direction K ₁ The paper container is folded and heat-sealed to produce a flat-top paper container. At this time, since the palm joint upper plate 15a is adhered to the inside of the joint palm joint plate 11a on the side of the continuous joint palm joint plate 14b, the top seal portion has a laminated sheet having four layers and a five layers. Will happen.

FIG. 2 (a) is a partial cross-sectional view illustrating an embodiment of the hermetic sealing method of the present invention. The pressure block plates 21 and 22 are repeatedly moved in arc-shaped moving directions R ₁ and R ₁ respectively. When operating and moving away from each other (moving to the position shown by the dotted line), the overlapping space portion is provided with an overlapped area of the cylindrical sleeve S to be hermetically sealed (for example, the palm joint plates 11a, 13a).
a, when the palm joint upper plate 15a and the interlinked palm joint plates 12b, 12b, 14b, 14b folded inside are inserted and subsequently approached (moved to the position shown by the solid line),
The overlapped regions of the tubular sleeve S to be hermetically sealed are sequentially pressed from both outer sides to hermetically seal them. Subsequently, when they are separated from each other, the hermetically sealed cylindrical sleeves S are taken out and the next separation interval portion is provided. By inserting the overlapping region of the cylindrical sleeve S to be hermetically sealed and repeating this operation sequentially, the top seal portion T (or the bottom seal portion B) of the plurality of cylindrical sleeves is hermetically sealed, and FIG. A paper container as shown in d) is obtained.

When the overlapped area of the cylindrical sleeve S to be hermetically sealed is inserted between the pressure block plate 21 and the pressure block plate 22, a portion in which ferrites 25 and 26 described later are embedded is hermetically sealed. It is important to set the cylindrical sleeve S so as to abut the portion of the palm-applied upper plate 15a in the overlapping region to be superposed. In this manner, the five-layered portion of the top sealing portion T is also appropriately heated, and the entire top sealing portion is uniformly heated and hermetically sealed (see FIG. 2B).

As shown in the partial side sectional view of FIG.
In one embodiment of the hermetic sealing method of the present invention, each pressure block plate
Reference numeral 22 is made of a non-conductive material such as FRP, bakelite, and ceramic. A pair of pipe-shaped high-frequency coils 23 and 24 having three sides embedded in a pressure block plate are provided with their surfaces facing each other exposed. Ferrites 25 and 26 are partially embedded in the pressure block plate below the high-frequency coils 23 and 24 so as to be in contact with the high-frequency coils, except for one surface facing the same.

This ferrite has as high a saturation magnetic permeability as possible at a working frequency and a small hysteresis (a small amount of heat generation), and a sintered product can be particularly preferably used. The exposed high-frequency coil surface and the ferrite surface form the same plane as the pressure block plate surface, and constitute sealing surfaces 27 and 28.

The high frequency coils 23 and 24 are
A power supply unit 31, a high-frequency generator 32, and an on / off switch 33 are connected in series to an intermediate portion of the power supply wiring 30.

When the pressure block plates 21 and 22 move in the arc-shaped movement directions R ₁ and R ₁ and move away from each other, a rotary cam provided in a drive system that moves the pressure block plates 21 and 22. The ON / OFF switch 33 is opened in synchronization with the moving operation via a relay relay circuit or the like by a timing switch such as a mechanism, a limit switch, a proximity switch, or the like. Since no high frequency is generated by the heater 32, no heat is generated.

In the next operation, the pressure block plates 21 and 22 move in the arc-shaped movement directions R ₁ and R ₁ to approach each other,
The polymerization area to be hermetically sealed (for example,
13a, the palm top plate 15a and the inwardly connected palm pasted plates 12b, 12b, 14b, 14b) which are folded inward, when a timing switch such as a rotary cam mechanism, a limit switch, a proximity switch or the like is used, a relay relay circuit, etc. , The on / off switch 33 is closed and operated in synchronization with the approaching movement operation to generate the high frequency by the power supply unit 31 and the high frequency generator 32 on the sealing surfaces 27 and 28,
While pressing the polymerization region to be hermetically sealed by 28, heat treatment is performed by the generated high frequency to heat and fuse the synthetic resin layer on the inner surface of the polymerization to perform fusion, and a paper container as shown in FIG. can get.

[0029]

EXAMPLES Examples of the present invention will be described below more specifically. << Experiment 1 >> Case where the overlapped portion (connecting plate) due to the lamination of the laminated sheets is located at the end of the paper container. <Example 1> First, [outside the container] polyethylene resin (2
0 μm thickness) / paperboard (basis weight 230 g / m ² ) / polyethylene resin (18 μm thickness) / aluminum foil (7 μm thickness) /
A predetermined bending line is formed on a laminated sheet having a layer structure composed of stretched polyester resin (12 μm thickness) / polyester resin (60 μm thickness) [inside of the container] using a generally used flatbed type punching machine or the like. While punching into a desired shape to produce a paper container blank, and further using a frame sealer or the like to produce a paper container sleeve S in which one end of the blank body joining portion was skived (FIG. 4).
(See (a)).

Next, the sleeve S for a paper container is set in a liquid paper container forming / filling / sealing machine having a sealing jaw 20 shown in FIG. 1 (with a high-frequency sealing device according to the present invention). The contents were filled in a prescribed amount sequentially, and finally the top was hermetically sealed by a high-frequency sealing method in accordance with the above-described top sealing method to produce a paper container filled with the contents (detailed working steps were omitted). In addition, the sealing condition of the top part is a sealing pressure of 5 kg.
f / cm ² , voltage 180V, current 14A, power 2
520 W, oscillation time 1.0 second.

<Comparative Example 1> A liquid paper container forming and filling machine equipped with a conventionally used high frequency sealing device (a type in which ferrite is not embedded in a pressure block plate) was used.
The same paper container sleeve S as in Example 1 was set, the bottom was hermetically sealed in the same manner as in Example 1, and the contents were filled in a prescribed amount in order. Finally, the top was hermetically sealed according to the following high-frequency sealing conditions. A paper container filled with the product was produced. Top sealing conditions: sealing pressure 5 kgf / cm ² , voltage 175 V, current 7 A, power 1225 W, oscillation time 1.0 second

<Comparative Example 2> The same paper container sleeve S as in Example 1 was set in a conventionally used liquid paper container forming, filling and sealing machine equipped with a hot air type sealing device.
As in Example 1, the bottom was hermetically sealed and the contents were filled in a prescribed amount sequentially, and finally the top was hermetically sealed under the heat sealing conditions described below to produce a paper container filled with the contents. Top sealing conditions: sealing pressure 5 kgf / cm ² , hot air temperature 400 ° C, hot air pressure 60
mmAq

[Experiment 2] In the case where the overlapped portion (connecting plate) due to the lamination of the laminated sheets is located substantially at the center of the paper container <Example 2> The laminated sheet having the same layer configuration as that of Example 1 was used. In the same manner as in Example 1, a paper container sleeve S ′ in which the connecting plate was positioned substantially at the center of the paper container was produced. Detailed description is omitted (see FIG. 4B).

Next, a paper container forming / filling and sealing machine (with a high frequency sealing device according to the present invention) having pressure block plates 21 and 21a as shown in FIGS. 3 (a) and 3 (b) is used. A paper container in which the sleeve S 'is set, the bottom is hermetically sealed, the contents such as juice are sequentially filled in a prescribed amount, and finally the top is hermetically sealed by the high frequency sealing method by the above-described top sealing method and the contents are filled. Was prepared. The sealing conditions at the top were as follows: sealing pressure 4k
g / cm ² , voltage 200V, current 15A, power 3
000 W, oscillation time 0.5 second.

<Comparative Example 3> The same paper container sleeve S as in Example 2 was applied to a conventionally used paper container forming / filling and sealing machine equipped with a high-frequency sealing device (a type in which ferrite was not embedded in the pressure block plate). 'And set Example 2
The same paper container sleeve S ′ as above is set, the bottom is hermetically sealed in the same manner as in Example 2, and the contents are filled in a prescribed amount sequentially. Finally, the top is hermetically sealed according to the following high-frequency sealing conditions, and the contents are sealed. A filled paper container was made. In addition,
The sealing conditions at the top were: sealing pressure 7 kg / cm ² ,
The voltage was 200 V, the current was 15 A, the power was 3000 W, and the oscillation time was 1.0 second.

<Comparative Example 4> The same paper container sleeve S 'as in Example 2 was set in a conventionally used liquid paper container forming, filling and sealing machine equipped with a hot air type sealing device. The bottom was hermetically sealed and the contents were filled in a prescribed amount in order, and finally the top was hermetically sealed under the following heat sealing conditions to produce a paper container filled with the contents. Top sealing conditions: sealing pressure 5 kgf / cm ² , hot air temperature 400 ° C, hot air pressure 60
0mmAq

The sealing condition of the top seal portions, the degree of scorching of the paper, and the degree of filling of the resin in the joint portions where the palm joint plates 11a and 13a were joined were visually observed by observing the top seal portions of the six types of paper containers prepared above. The integrity of the seal was checked. Table 1 shows the results. Judgment of the result Seal status ○… Good ×… The overlapping part of the aluminum foil does not adhere ××… Does not adhere at all The degree of scorch of paper ○… No scorch ×… There is scorch Resin burial, material destruction ○… Paper joint The resin is completely buried and the material is not destroyed. △… The bonded part of the paper is not completely buried, and no material destruction has occurred. ×… Material destruction has occurred.

[0038]

[Table 1]

From the results in Table 1, it can be seen that the paper container hermetically sealed using a high-frequency sealing device in which ferrite is embedded in a pressure block plate has a completely sealed resin at the joint, and the seal is completely sealed. It was performed, and the appearance was found to be beautiful (Examples 1 and 2).

[0040]

As described above, by using the pressure plate in which the ferrite is embedded in the seal jaw, a perfect hermetic seal can be achieved even in a paper container having a seal portion having a different number of aluminum foil layers. In addition, it has become possible to fill and seal paper containers using a polyester resin as a sealant. Furthermore, in the conventional filling and sealing step, two steps of a heating (hot air) step and a sealing step were required,
According to the present invention, only one heating (high-frequency) sealing step is required, and the filling speed is increased.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an example of a seal jaw used in the present invention.

2A is an explanatory view of the movement of a seal jaw during hermetic sealing as viewed from a cross section taken along the line AA ′ of FIG. 1, and FIG. 2B is a seal viewed from a cross section taken along the line BB ′ of FIG. It is explanatory drawing of a jaw, (c) is explanatory drawing which looked at the overlapping state of the lamination sheet of the upper end part of a paper container sleeve from the plane.

FIGS. 3A and 3B are explanatory views showing how a laminated sheet bites into a seal bar at the time of hermetically sealing according to a second embodiment of the present invention. FIG. 3A is a side view of a pressure block plate side on which a high-frequency coil is mounted. (B) is an explanatory side view of the pressure block plate side on which the high-frequency coil is not attached, and (c) is an explanatory view showing the overlapping state of the aluminum foil of the sleeve from a plan view.

4A is an explanatory diagram of a paper container sleeve used in an embodiment of the present invention, and FIG. 4B is an explanatory diagram of a paper container sleeve used in another embodiment.

FIGS. 5A to 5D are process explanatory diagrams illustrating a general method of hermetically sealing a liquid paper container.

[Explanation of symbols]

 A {side wall portion B} bottom seal portion T {top seal portion S} cylindrical sleeve 1, 2, 3, 4 {side wall plate 5} coupling plate 11, 13 {top plate 11a, 13a} {Gap palm plate 12, 14} Isosceles triangular plate 12a, 14a {Connecting triangular plate 12b, 14b} Link joint palm gluing plate 15} Linking upper plate 15a {Gashom sticking upper plate 20} Seal jaws 21, 21a, 22 ‥‥ Pressure block plate 23,24 ‥‥ High frequency coil 25,26 ‥‥ Ferrite 27,28 ‥‥ Seal surface 30 ‥‥ Power supply wiring 31 配線 Power supply unit 32 部 High frequency generator 33 ‥‥ On / off switch

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (Reference) B32B 27/32 B32B 27/32 Z 27/36 27/36 29/00 29/00 B65D 5/40 B65D 5 / 40 B // B29C 65/04 B29C 65/04 B29K 23:00 67:00 305: 00 B29L 9:00 F term (reference) 3E060 AA03 AB04 DA25 EA03 3E075 AA09 BA03 BA92 DD13 DD32 DD47 GA04 3E094 AA03 BA02 CA25 DA01 FA25 HA02 HA08 4F100 AB10C AK03B AK41D BA04 BA05 BA07 BA10A BA10D DG10A EJ61 EK00 GB16 GB23 JL12 4F211 AA03 AA24 AD03 AG03 AH56 AJ02 TA01 TC13 TD11 TD20 TN13

Claims (4)

[Claims] 1. A laminated sheet comprising a paperboard substrate, a polyester resin layer as an innermost layer, an aluminum foil layer as an intermediate layer, and a polyolefin resin layer as an outermost layer, and an inner layer at one end of the laminated sheet. And a method of hermetically sealing a tubular paper container in which the outer layer at the other end is joined by heat fusion, wherein one of the joining portions of the laminated sheet tubular portion is laminated in advance by a predetermined length from the tip. A method for hermetically sealing a paper container in which half of the thickness of the sheet is removed from the paper layer, and the remaining portion is folded from the inside to the outside of the removed portion to protect the paper end surface, wherein the hermetic sealing method uses a high-frequency sealing device. Using a seal jaw in which a ferrite is partially embedded in a high-frequency coil portion as a seal jaw of a high-frequency seal device, wherein innermost layers of the paper container are separated from each other. Rui hermetic sealing method of a paper container, which comprises sealing the innermost layer and the outermost layer by high-frequency sealing method. 2. The high-frequency sealing device is characterized in that ferrite is partially embedded in both sealing jaws on the side of the high-frequency sealing device on which the high-frequency coil is mounted and on the receiving jaw on which the high-frequency coil is not mounted to perform high-frequency sealing. The method for hermetically sealing a paper container according to claim 1. 3. The method according to claim 1, wherein ferrite is embedded in the sealing jaws according to the folded shape of the paper container. 4. An apparatus for forming a paper container using the hermetically sealing method according to claim 1, 2 or 3.